Forty-eight percent of registered voters who watched the debate in Dansville, Ky. said that Ryan was the winner, while 44 said Biden ended up on top. That's within the poll's margin of error of 5 percentage points.

Keating Holland, polling director for CNN, urged caution to those trying to derive too much meaning from the poll, highlighting the limits of such a survey. Holland also acknowledged that the poll's sample of debate watchers included more Republicans than the average of recent CNN polls.

The CNN poll was conducted immediately after the debate using live phone interviews with 381 registered voters nationwide who watched the debate.